This invention relates generally to an improved liquid crystal composition, and in particular to an improved liquid crystal composition suitable for multiplex operation and to a liquid crystal display device including the liquid crystal composition.
Liquid crystal display devices including liquid crystal display elements have found increasing utility in applications such as alpha-numeric displays and graphic displays. Liquid crystal display devices which are adapted for multiplex operation, using conventional nematic liquid crystal composition have experienced drawbacks in operation. For example, it is desirable that such liquid crystal display cells operate at a duty ratio of about 1/16. It is also preferable that the electronic devices operate at low voltage supplies, preferably no more than about 5 V.
In multiplex display devices, when the display device is operated at a duty ratio of about 1/16, the threshold voltage rises, causing the central driving voltage, V.sub.op, to also rise. When the V.sub.op rises it generally rises to the range of up to about 8 V. Such a high voltage exerts a heavy drain on the driving circuit and can cause the voltage margin M to assume a negative value. These conventional liquid crystal cells also retard the display response speed, thereby contributing to a general discoloration of the liquid crystal display, marred display and reduced display contrast. The retardation in the display cell affects the display appearance, e.g. whiteness and brightness. Retardation depends upon display cell thickness and liquid crystal optical anisotropy.
Fabrication of liquid crystal cells having thicknesses in the range of 4 to 6 microns is now possible. In order to provide a suitable retardation R, to allow for optimum display whiteness and brightness it is necessary to provide liquid crystal compositions having optical anisotropy in the range of 0.10 to 0.12, which can also withstand the normal parameters of operation of liquid crystal display devices, such as working temperature range, low operating voltage, large voltage margin, and rapid response speed.
Accordingly, it is desirable to provide a liquid crystal composition having an optical anisotropy in the range of about 0.10 to about 0.12 and other advantageous properties and to provide a liquid crystal device including such compositions.